When most people think of wastewater treatment, they probably don’t think of rocket science. Well, at Stanford we are bringing rocket technology to wastewater treatment. Sounds crazy, right? It turns out the two fields have a lot in common. In the propulsion field, rocket scientists design the most powerful machines on the planet that use the chemical energy of fuels to take humans to space. Rockets get their power by tapping into the chemical energy in the bonds of fuels. Like rockets, wastewater treatment facilities can in effect do the same thing; exploit the chemical energy in the molecules in waste streams to generate energy. And most wastewater streams have a lot of potential energy.
The energy in wastewater treatment most commonly comes from carbon containing organic matter. Bacteria convert organic matter into methane, a combustible fuel that can be burned to generate power. In addition to carbon containing organic matter, there is also nitrogen in wastewater. Unfortunately, current treatment processes don’t recover energy from waste nitrogen. But what if we could convert waste nitrogen into a combustible gas, just like converting organic matter into methane? It turns out we can! That’s where the rockets come in. Bacteria are capable of converting waste nitrogen into nitrous oxide... yeah, nitrous oxide. The same stuff your dentist gives you, although dentists usually call it “laughing gas”. It’s also the same gas racecar enthusiasts use to supercharge their engines, although they call it “nitrox”. It’s also the same gas that has been used for decades in rockets. In fact, Space Ship One, the first privately manned spaceplane that is paving the way for sub-orbital space flights open to the public, used nitrous oxide in its rocket motors. It’s powerful stuff and we can get it for free from wastewater! At Stanford we are developing a way to get bacteria to convert waste nitrogen into nitrous oxide, thus enabling energy recovery from both waste carbon and nitrogen. By producing nitrous oxide, we could essentially “supercharge” wastewater treatment, kind of like a nitrox turbocharged racecar.
Wastewater treatment may not take us to the moon, but it can provide a serious amount of free and clean energy. Considering that the treatment of wastewater consumes 3% of U.S. energy supply and wastewater treatment plants are often the highest energy expenditure for cities, generating power from wastes seems like a really good idea.